Contemporary packet-oriented communications networks—also referred to as “data networks”—have previously been designed essentially for transmitting packet streams which are also referred to in the specialist field as “data packet streams”. Hence, there is usually no need for an ensured transmission service quality level. The transmission of the data packet streams thus takes place, for example, with delays whose timing fluctuates as the individual data packets of the data packet streams are usually transmitted in the sequence of their network access, i.e. the timing delays become longer the more packets are to be transmitted by a data network. In the specialist field, the transmission of data is therefore also referred to as a transmission service without real time conditions or as a non-real time service.
In the course of the convergence of line-oriented speech networks and packet-oriented data networks, real time services, i.e. transmission services under real time conditions such as the transmission of speech information or moving image information, are increasingly also being implemented in packet-oriented communications networks, i.e. the transmission of the real time services which have previously usually been transmitted in a line-oriented fashion is being carried out in a packet-oriented fashion, i.e. in packet streams, in a convergent speech-data network. These packet streams are also referred to as “real time packet streams”. Here, the problem arises that for an implementation of a real time service which is embodied as a packet-oriented transmission a high level of service quality is necessary for the implementation to remain comparable in, terms of quality with a line-oriented transmission. In particular, a minimum—for example <200 ms—delay without fluctuations in the delay is important as real time services generally require a continuous stream of information, and cannot compensate a loss of information, for example due to packet losses, by repeated transmission of the discarded packets. As these service-quality-level requirements basically apply to all communications networks with packet-oriented transmission, they are independent of the specific refinement of a packet-oriented communications network. The packets can consequently be embodied as Internet packets, X.25 packets or frame-relay packets, but also as ATM cells. Data packet streams and real time packet streams are, in this case, exemplary embodiments of traffic streams which are transmitted in communications networks.
For the transmission of speech and image information via the packet-oriented Internet—also referred to as “VoIP”—protocols for a transmission over the Internet have been proposed in the international standards—in particular the H.323 standard. Here, the network is divided into a plurality of “H.323” zones in which what are referred to as “gatekeepers” are respectively provided for                converting E.164 telephone numbers to computer names and their Internet addresses,        permissibility checking for incoming and outgoing conversations,        administration of transmission capacities,        registration of H.323 terminals.        
However, as there is no ensured service quality level for the Internet transmission in the current H.323 standards, the current VoIP technology has the disadvantage that the quality of the transmission of speech and images decreases if the number of packets to be transmitted by the Internet rises. In this respect, the IETF (Internet Engineering Task Force) has proposed that a plurality of service classes should be introduced in the packet-oriented Internet which previously did not ensure any service quality levels, said proposal being in Blake et. al., “An Architecture for Differentiated Services”, RFC 2475, 1998, ftp://venera.isi.edu/in-notes/rfc2475.txt and in Nichols et. al, “Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers”, RFC 2474, 1998, ftp://venera.isi.edu/in-notes/rfc2474.txt. Such an Internet is also referred to as ‘DiffServe network’. Here, the individual packet streams are each assigned to a specific service class and, depending on their service class, are transmitted by the transmission nodes of the Internet with or without priority over packets of other service classes. The service quality level which is required for the real time services can thus be ensured, for example, by virtue of the fact that the associated real time packet streams are assigned to a service class which is transmitted with priority by the nodes of the Internet—the real time packet streams are thus prioritized with respect to the data packet streams.
By forming a class of traffic streams which are to be transmitted with priority, a (virtual) separate communications network for the transmission of the prioritized traffic streams with a separate overall transmission capacity, which comprises part of the overall transmission capacity of the Internet, is formed within the Internet. Here, that capacity which is necessary to transmit the traffic streams which are just still capable of being transmitted without loss of traffic is considered to be the overall transmission capacity of a communications network which is composed of transmission nodes and paths. In other words, this means that it would not be possible to transmit a further traffic stream in the communications network without a loss of traffic. The still available transmission capacity of a given route between two transmission nodes of the communications network accordingly depends not only on the traffic which is transmitted directly between these two transmission nodes but also on that traffic which is transmitted at least partially along the given route as a consequence of a transmission along other routes in the communications network.
In a priority-controlled transmission, network access control is basically necessary at least for the prioritized traffic as the requested service quality level can only be ensured if no more prioritized traffic is fed to the communications network than the maximum which can be transmitted by said communications network. For this purpose, network access devices—also referred to as “edge devices” or also “access nodes” from the point of view of the communications network—are proposed for the Internet with a plurality of service classes, said devices performing the network access control. In this context, the edge devices can                control the volume of the traffic fed to the communications network by means of packet streams;        set priority markers in the packets corresponding to the priority of their packet streams;        monitor priority markers of packet streams and if appropriate correct them if the packets are already marked with priorities;        monitor the transmission capacity of prioritized packet streams.        
Hitherto, how a permissibility check of a transmission of a packet stream which has been applied for, for example, at a gatekeeper or an edge device is to be brought about in this context has not been regulated.
A method in which resources which are necessary for the transmission of a packet stream are requested from each transmission node of a communications network using a reservation protocol RSVP, and the transmission of the packet stream does not occur if at least one transmission node cannot make available the requested resources is known. In this context, the permissibility check is checked in the transmission nodes taking into account only capacities which can be determined locally, i.e. usually the capacities of the outgoing transmission paths and/or channels. In addition, the reservation protocol RSVP must be implemented in each—i.e. even the internal—transmission node of the communications network.